“Reflectarray” antennas were introduced in the 1950's as an alternative to parabolic or spherical reflector antennas. The idea underpinning this antenna typology consists in replacing the continuous and curved reflective surface of the parabolic reflector with a (generally periodic and planar) array of passive electromagnetic scatterers, that can be easily produced in printed technology. In a reflectarray, the curvature of the reflector is simulated by the phase shift introduced by the various scatterers, a phase shift which in turn depends on the form and dimension thereof. As with reflector antennas, it is also possible to use systems comprising a plurality of cascaded reflectarrays, for example in the Cassegrain or Gregorian configuration.
Reflectarrays have intermediate characteristics between those of reflector antennas and those of array antennas. They are particularly suitable for use in satellites and radars, and can be used to make different types of antenna, and in particular “pencil beam” antennas, that are able to radiate electromagnetic energy in very restricted angular ranges, “multi beam” antennas, which offer the opportunity to produce with a single radiating structure a plurality of radiation patterns with different characteristics, and “steered beam” antennas. In the two latter cases, multiple feed systems are typically used.
Publications [1-3] describe advanced synthesis methods which can be used to obtain shaped beam “reflectarray” antennas, with radiation patterns appropriately shaped so as to obtain a specific illumination, typically for satellite applications.
Publication [4] describes a configurable reflectarray, in which the radiation pattern can be modified dynamically, by acting on the phase introduced by the electromagnetic scatterers by means of “varactor” diodes integrated into said elements, the bias voltage of which may be varied.
Publication [5] describes a reflectarray able to control two linear polarizations simultaneously.
Reflectarrays are generally planar (the scatterers are arranged on a plane surface, or exceptionally on a plurality of non-parallel plane surfaces) and periodic (the scatterers are arranged on a periodic grid), which means that particularly effective synthesis algorithms can be used. Publications [6] and [19] describe non-planar, but nonetheless periodic reflectarrays, in the sense that the projection of the scatterers on a plane is in fact periodic.
Publication [20] describes a “sparse” planar reflectarray, in which the scattering elements are arranged on a uniform grid, but some of them are eliminated.
Publication [21] describes a planar and aperiodic reflectarray synthesized by means of a genetic algorithm.